1. Field of the Invention
The present invention relates to method and apparatus for effecting controlled thermal contraction or shrinkage of zonnular tissue fibers to provide a non-invasive reversal of presbyopia , by means of a selective laser which is focused and delivered by a special device.
2. Brief Description of the Prior Art
Presbyopia has been a challenging disease for medicine. Eye glasses and contact lens are the most common method of compensating for presbyopia. Multifocal intraocular lens also have been employed but restricted to cataract patients. These procedures merely compensate for presbyopia, instead of restoring accommodation. Therefore, the suitable procedures for presbyopia patients to be cured are limited to those methods which involve reversal of presbyopia by acting upon the area of lens, zonnulas, ciliary body, and sclera. Reshaping the cornea with an excimer laser to form bifocal shape produces glare, halos and unacceptable monocular diplopia.
Procedures for presbyopic correction using insertion of rigid bands were proposed by R. A. Schachar in U.S. Pat. Nos. 5,529,076, 5,489,299 and 5,722,952. In the prior arts of Schachar a multitude of claims were made, being the great majority restricted to abstractions. Specially in U.S. Pat. No. 5,503,165 it claims to cover all lasers from the electromagnetic spectrum for contracting the zonnulas and reversing presbyopia. Contracting the zonnulas to reverse presbyopia is a tangible medical method. However the zonnulas are deprived of pigment and therefore can not be heated by many of the lasers cited by Schachar""s prior arts.
It is further believed that Schachar had incorrectly assumed that all lasers will act on pigment-free tissues such as the zonnulas. Many of the lasers cited by the prior arts of Schachar are photoablative and simply would not cause thermal effects on the zonnulas. Furthermore, in these prior arts, there was no mention of any specific laser parameters which is capable of causing the thermal shrinkage of the zonnulas and only abstract idea was suggested which covered all existing lasers. On the other hand, one of the present inventors (Martins), filed a U.S. patent application called xe2x80x9cLaserthermozonnuloplastyxe2x80x9d on Jan. 23, 1997, U.S. appl. Ser. No. 08/792,848, describing the idea of laser presbyopia reversal. This patent was abandoned later by the present author in virtue of the fact that, just as Schachar""s, it was only an abstraction and lack of specific laser parameters and the focusing means to restrict the laser thermal energy to the target tissue (zonnulas). Without specifying the laser parameters and its delivery means, the abstraction suggested by the prior arts will not provide a clinically useful system. Furthermore, non of the idea suggested by the prior arts has been tested by a device.
One of the present inventors (Lin) also proposed the use of lasers for presbyopic corrections by removal of a portion of the scleral tissue over the ciliary body, U.S. patent application Ser. Nos. 09/189,609 and 09/303,673. These methods, however, are invasive and laser ablation depth is critical for the clinical outcome and safety.
It is one of the objects of the present invention to provide a laser system which offers a non-invasive method and apparatus to correct presbyopia. Our present invention came from the expertise of one of the inventors in ophthalmology (Martins) and the knowledge of the other in laser physics (Lin). It is specific in the mode and applicable principles. It describes the manner and process of making and using a laser and related accessories in order to achieve zonnular contraction, concisely and exactly. The proposed method shall apply to out-patients and involves no implanting, no tissue cutting or ablating, no suturing, no bleeding and can be performed easily and fast.
It is yet another object of the present invention to provide the details of a mean to deliver the laser to the targeted-area without significant damage to the other surrounding tissues. Specific laser spot size, beam focusing and tissue absorption are critical in the proposed method for safety and clinical outcomes. The desire is to heat selected areas of rich in collagen tissue to a shrinkage level, but without damage or destruction of either the target or surrounding tissues. In other words, the selective laser is used to irradiate the zonnulas tissue with energy such that the temperature of the collagen tissue is raised sufficiently to cause the tissue to shrink but not so high as to cause any substantial damage. The thermal shrinkage of the selected zonnulas area of the eye will cause the zonnulas to change its shape, decreasing its length, and then reverse presbyopia.
It is yet another object of the present invention to provide a laser system which is portable, compact and easy to be integrated with a slip lamp.
Other than these above mentioned, no other author of our knowledge had ever proposed or designed a device for contracting the zonnulas for correcting presbyopia or presented anything beyond mere abstractions. To our knowledge we are the first ones to propose a practical medical device for successfully contract the human zonnulas.
The system proposed in the present invention consists of an infrared laser which is focused to the human zonnulas, where it will provoke a thermal contraction. It is attached to a slit lamp and shot through an ophthalmic gonio lens, aimed at the equatorial zonnulas and aided by a visible aiming laser that assists in focusing in the precise location. The laser has the characteristic of partial water absorption, not needing a chromophore (pigment) in order to produce a localized increase in temperature at the laser focual point. The increase in temperature in the beam pathway, due to partial water absorption, is far less than that obtained at the focal point due to the cone shape of the beam, which favors dissipation. In the present invention, the desire is to heat selected areas of rich in collagen tissue to shrinkage levels, but without damage or destruction of either the target or surrounding tissues. The thermal shrinkage of the selected zonnulas area of the eye will cause the zonnulas to change its shape, decreasing its lengths and reverse presbyopia. For the first time in medicine this process is being used and will be useful not only for correction of presbyopia but also any ophthalmic disease that requires focal heat in tissues with high water and protein content.
To achieve the proposed selected thermal shrinkage of the zonnulas and increase the accommodation of presbyopia patient, the system design must meet the following requirements: (1) the absorption of the laser beam in its propagation path inside the eye is optimal, not too high to cause damage other than the selected area to be shrinkaged, but high enough to cause the thermal effect on the selected area; (2) the laser beam shall be focused and enter the eye in a cone shape having the focal point near the selected target; and (3) the thermal shrinkage of the selected area shall cause the lens to change its shape such that the patient""s eye can accommodate to see both far and near. The zonnulas are considered to be relatively inert in its steady state, and while thermally induced contraction occurs by the process of this invention, temperatures are bellow the thermal traumatic or inflammatory thresholds. In absence of trauma, the dimensional collagen reconfiguration is believed to exhibit long-term stability .